Method of sintering ores



July 16, 1957 Filed April 7, 1953 4 Sheets-Sheet. 1

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S/N TER/NG Macy/N5 SCREEN F//VE S July 16 1957 J. c. BARNET-r ETAL2,799,573

METHOD oF SINTERING oREs Y Filed April 7, 195s 4 sheets-sheet 3 July 16,1957 J. c. BARNETT Erm. 2,799,573

METHOD OF SINTERING ORES Filed 'April 7, 1955 4 Sheets-Sheet 4 /0 /z /4/6 /a za Z2 96 czwr F550 /va/srz/Ff.

United States 2,799,573 METHOD oF SINTERING onus James C. Barnett,Dayton, l1io, and James D. Barnllill, Columbia, Tenu., assignors toMonsanto Chemical Company, St. Louis, Mo., a corporation of DelawareApplication April 7, 1953, Serial No. 347,372

6 Claims. (Cl. 75--5) phosphate ores by blast roasting on a vDwight `andLloyd sintering machine.

An object of the invention is to provide .an improved method ofsintering which results in a substantial in-v crease in sinterproduction and a substantial improve- 4ment in sinter quality ascompared to prior art methods of sintering.

Another object of the invention is to Provide an imfines, haveheretofore been mixed simultaneously, resulting in a sinter feed whichpossesses a rather'low burning rate, thus limiting the productionobtainable from the machine. In addition, this procedure has Vsufferedfrom excessively high maintenance on the mixing device `since therecycle material is very abrasive.

We have made the surprising discovery that the ilimita- Ationsencountered in ythe aforesaid method of sintering ores, and particularlyphosphate ores, are overcome by Ithe novel procedure hereinafterdescribed. In accordance with this procedure, finely divided ore, acarbonaceous fuel and water are first intimately and uniformly mixedtogether Vin a pug millor another suitable mixing device. Then at, orsubstantially at, the end of the mixing or pugging operation, recyclefines from a prior sintering operation are thoroughly blended with themixture of ore, fuel vand water. After completing this operation, the

v resulting feed'ischarged to the sintering machine and proved sinteringmethod in which higher sinter yields are' obtained when using theoptimum amount of water in the Ysinter feed rthan has been heretoforepossible vby the methods of the prior art.

An additional object of the invention is to provide an improved-sintering method :in which the maximum Eproduction previouslyobtainable by prior art methods is now obtainable by `using a sinterfeed having a much wider range of water content.

An additional object of the invention is to provide an impropedsintering method which permits burning tof isubstantially deeper sinterbeds and thereby increases the productive capacity of the sintermachine.

A further object of the invention is -to providean im' proved method ofsintcring involving the use of a sinter feed which permits higher gasflow through the bed and thus an increased flame propagation -rate witha correspondingly higher production rate and ywithout anii-ncrease inwindbox suction. v

Afstill further objectlof the invention is to provide au improved methodof sintering ywhich involves the; use of a sinter feed having improvedheat transfer charaeteristi-cs during sintering and which resultsindecreased wear on the mixer'during the mixingoperation. I

Other objects and advantages will become apparent to those skilled inthe art as the description-,of theinventiori proceeds. 7

in the sintering of ores on a Dwight and Lloyd. or equivalent sinteringmachine, a mix-ture ofore, carbonaceous fuel, water and recycle materialfrom ,the prior .operation of the machine is charged onto a moving grateand :ignited by a ame vwhile air is drawn downwardly Ithrough the grateinto wind boxes whichare connected to asouree of reduced pressure.wardly through the material :on the grate and thus combustionispropagated down ythrough this material. Once the bed is ignited, theignition flame is removed. and the fuel content lofythe bed continues toburn as additional air is forced through `the bed. .The heat from suchcombustion causes the' :fine ore to sinter together and form a porousaggregate.

In ,the sintering-of ores on a machine of this type, it

has been the practice to use a sinter feed prepared byy mixing 'togetherfinely ,divided ore, coke or other :carbonaceous fuel, a relativelysmall pr oportion of Vrecycle fines and water. These materials,including the recycle This serves to force the air downsubjected tosintering in the usual manner. The sintered product is then crushedbetween rolls, on a metal bar grizzly screen or another suitablecrushing device and screened to separate the fines from the oversizematerial Awhich Ais the desired product. The fines thus obtained arerecycled and used inthe manner previously described in the production ofkfurther quantities of sintered product.

For a more complete understanding of the instant invention, reference ismade to the accompanying drawings and the illustrative examplehereinafter presented.

'Figure l illustrates a ow sheet ofthe improved method of sinteringofthe instant invention.

.As a modification of the method illustrated in Figure 1, the sinteredproduct from the crushing rolls is passed through a `two-inch grizzlyscreen to separate a +2 material as sintered product and a 2" undersizedmaterial. This undersized material is treated on a Vibrating screen yandseparated into three fractions, namely, a -2/-{% sintered Vproduct whichis mixed with the +2 material, a -1'-8mesh material (recycle fines) anda .-8-mesh product (dust) which is incorporated with the finely dividedore, carbonaceous fuel and water and charged to the pug mill or anothersuitable mixing device. The -recycleliines are returned to the processin the manner shown inthe flow sheet.

"Figure 2 graphically illustrates phosphate sinter production as a'function of feed moisture when varied amounts ofrecycle fines wereadmixed with the sinter feed before and after pugging.

As indicated in Figure 2, curves A, B and C demonstrate the effect offeed moisture on phosphate sinter production when 0%, 10% and 20% byweight of recycle fines were'pugged in feed, whereas curves B and C'show the effect of feed moisture when 10% and 20% by weight of recyclefines were added after pugging the feed.

Figure 3 graphically illustrates in curves F, Fand G, G phosphate sinterproduction as a function of feed moisture when 420% ,fines were admixedwith different types of sinter feeds before and after pugging.

figure -4 graphically illustrates in curves D, D and E E phosphatesinter production as a function of feed moisture and bed depth when therecycle lines were admixed with a typical sinter feed before and afterpuggingvThe description fof a typical method and apparatus used inpracticing the instant invention will now be given.

.The apparatus used in practicing this invention consisted essentiallyof a laboratory pug mill and a sinter pot pilot plant.

The pug -millhad a 24-inch diameter shell which was 32 inches long androtated at 9.1 R. P. M. Inside this Shell .there was an .eccentricallymounted shaft containing four rows of S-inch cutter blades (12 bladesper 2,799,573 e N p e row) which rotated at a speed of 177 R. P. M. andin an opposite direction from the shell.

The sinter pot pilot plant consisted of an 18-inch x l8-inch pot, whichwas l1 inches in depth and whose sides tapered downward to a l41/z-inrchx 14Vzinch grate. Underneath the grate there was provided a 12- inchwind box with a 4-inch exhaust main about which the pot was pivoted sothat it could be inverted to dump the charge. A blower fan was employedto draw air through the wind box at a rate which was measured by anorifice and controlled by an externally located control valve. Above thesinter pot there was a retractable ignition hood which was fired by apropane-air mixture.

The sinter feeds were prepared from stocks ofV sinter grade phosphatematrix, phosphate concentrates, recycle fines, recycle dust andanthracite dust. They were all prepared in the same manner except inthose instances where the fines were withheld from the pug mill andmixed with the feed after the pugging operation. In these cases, thefines were mixed with the pugged feed by pouring the two through al-inch sample splitter, simultaneously. After the first split the twohalves were vsimultaneously poured into a large pan and then poured backthrough the splitter and combined again.

The two types of sinter feeds were charged to the sinter pot pilot plantin exactly the same manner, that is, sixty pounds of the wet feed,except in those runs using sinter beds of varying depths, was chargedinto the sinter pot in such a manner as to provide a bed depth of about6% inches. After a layer of coke fines had been sprinkled over the topof the charge to assure its complete ignition, a reduced pressure of 8inches of water was produced in the wind box by opening the air flowcontrol valve. The gas flow rate at this standard 8-inch suction wasused as a criterion of the beds initial po- Table I Sinter Feed Anal-Gas Flow (Standard ysis Cu. Ft. Per Min.) Percent lbs. +8M Sinter-8-Mesh Min-Ft.2 Cake, After Grate Comments H20, per- C, per- Averagelbs. Crushing Area cent cent 8 H2O After Ignition 42 gg 0% Fines PuggedIn Feed, 70 30-70 Ratio.

10% Fines Pugged In Feed,

30-70 Ratio.

10% Fines Added After Pugging Feed, 30-70 Ratio.

% Fines Pugged In Feed,

-70 Ratio.

20% Fines Added After Pngging Feed, 30-70 Ratio.

20% FinesPugged I n Feed,

0-100 Ratio.

20% Fines Added After Pngging Feed, 0100 Ratio.

20% Fines Pugged In Feed,

-50 Ratio.

20% Fines Added After Pngging Feed, 50-50 Ratio.

20% Fines Pugged In Feed, 30-70 Ratio, 72 lbs. Charge, B-Inch Bed.

20% Fines Added Aftercomoccolenenooooocnoenooenoocenocnoooenoomenocenmmcxcoccnonwoocenmcnomoxoo'armas-vs Yro'sity. At this point the ignition hood was :placed over thesinter pot and the wind box control valve opened further to allow thefull application of reduced pressure.

The sinter bed was ignited for 40 .seconds using a n flame temperaturevof about 1350 C., whereupon the ignition hood was removed. In exactly 5minutes after vignition commenced, the blower fan was .cut off. Duringthis period, the gas fiow rate, the wind'box suction 'and the wind boxtemperature were measured at one minute intervals. The sinter pot wasthen inverted and the cake dumped into a heavy metal pan. After therecovered charge had been weighed, the sinter cake was scraped free ofall non-sintered material and weighed. When the sinter cake had cooled,it was crushed in a ,l-inch roll crusher (7/s inch roll spacing). Thecrushed fragments were screened through 3/s-incll and 8-mesh screens,the percentage of -S-mesh material being used as'a Acriterion of sinterquality.

The instant invention is further illustrated by .the following 'specificexample which clearly demonstrates the advantages obtained by admixingrecycle fines with the sinter feed after pugging. In this example, thesintering operation was carried out in the manner described above, usinga sinter feed containing 0%, 10% and 20% by weight (dry basis) ofrecycle fines.

The properties of the sinter feed and sinter bed, the amount of carbonused and the quantity of sinter produced `are given in Table I.

The expression ratio as used in ythis table has reference 4to the weightratio vof thephosphate sinterlgrade matrix to phosphate concentrates. f

All feeds had same weight of fuel vadded except those used for `deeperbed depths wherefuel was proportionately increased. Variations `incarbon content shown in the above table are due to experimental andanalytical error.

The results recorded in this table are graphically illustrated inFigures 2, 3 and 4 of the accompanying drawings. From these figures, itwill be observed that, regardless of the moisture content of the sinterfeed, the amount of fines and the feed 'proportions used, or the beddepth, the sinter production was consistently increased when the recyclefines were added after the pugging operation.

In the practice of the instant invention, the recycle fines, i. e., the-%/|8mesh materials, are employed in an amount varying from about 5% toabout 25% by weight of the sinter bed or, more specifically, from aboutto about 20% by weight and within these limits about by weight ispreferred.

The fuel content of the sinter bed varies with the ore being sintered,but in general it falls within the range of about 2% to about 15 or,more specifically, in the range of about 7% to about 12% by Weight ofthe bed.

More particularly, in the sintering of phosphate ores, the practice isto use a fuel content of about 6% to about 12% or, more specifically,about 7% to about 8% by weight of the bed.

Illustrative examples of fuels which may be used in the practice of theinstant invention are coke, coal, peat, charcoal, hydrocarbons and othercarbon-containing fuels.

The amount of water used in preparing the sinter feed may vary withinthe range of about 5% to about 21% by weight or, more specifically,within the range of about 16% to about 20% by weight of the sinter bed.Within the above range, a sinter feed moisture content of about 18.5% byweight is preferred.

The optimum percentages and percentage ranges stated above apply tophosphate sintering and it is to be understood that these variables willvary with the ore being sintered. Suffice it to say that they may bereadily determined in each case by those skilled in the art and so noattempt Will be made to state them here.

The admixing of the recycle fines with the sinter feed 6 substantiallyYat the 'end of or 'after the pugging opera- "tion, instead of before orduring the principal portion lof the pugging operation leads to a numberof highly advantageous results.

For example, when using an optimum feed moisture of about "18.5%, themaximum yield of sintered product obtained by the method of the instantinvention is invariably higher than that obtainable by the prior artmethod in which the recycle fines are pugged in the feed. lThis fact isclearly demonstrated by the accompanying graphs and also by thefollowing typical experimental results.

Fines Pugged Fines Added Optimum I nSinter AfterPuggng Type of SinterFeed (Matrix. Feed Feed, Sinter Feed,

to Concentrate Ratio) .Moisture Sintered Sintered Percent ProductProduct Produced, Produced,

bs. Lbs.

0-100 feed ratio 18. 5 29. 8 32.2 i30470 feed ratioA 1s. 5 31.8 33. 3fso-soteed'ratim 18.5 30. 8 33. 5

y"Moreover, .by the method of the instant invention, the maximum-sinterproduction achieved by the prior art .methods at Jan optimum feedmoisture of 18.5% may be obtained .by .the present invention over awider range :of :sinter feed moisture content. As evidence of this.fact, reference is made to the following typical experimental data.

Feed Moisture Feed Moisture Resulting In Resulting In Typeof Sinter Feed(Matrixto Con Maximum Sin- Equivalent centrate Ratio) ter ProductionMaximum Sin- By Prior Art 'ter Production Methods By Method Of InstantInvention Percent Percent 18. 5 16. 6-20. 2 18. 5 16. 8-20. 0 50-50 feedratio. 18. 5 16A-.19.4

In view of the normal fluctuations which occur in the sinter feedmoisture, the widening of the effective feed moisture range has thedesirable effect of increasing sinter production and facilitating thecontrol over the sintering operation.

In addition, the method of the instant invention makes passible the useof deeper sinter beds because of the higher sintering rate which may beemployed. This burning of deeper beds not only. results in increasingthe productive capacity of the sinter machine but lowers the percentageof recycle to the machine. The reason for this is that thick sintercakes have less abrasive surface and therefore yield less dust andfines. Thus, the addition of fines after pugging in accordance with thisinvention provides increased sinter production and better sinterquality.

Furthermore, the recycle fines retain their jagged edges when they areadmixed after pugging; Whereas, when they are pugged with theotherrcomponents of the feed, they are coated with mud and convertedinto round, wet pellets which have poor heat transfer properties.

Also, the recycle fines are very abrasive and cause excessive wear andtear on the cutter blades of the pug mill when they are pugged in thesinter feed. In contrast thereto, the addition of the recycle fines tothe sinter feed at, or substantially at, the end of the puggingoperation results in a substantial reduction in the cost of maintainingthe cutter blades.

What is claimed is:

1. The method of sintering ores, which comprises intimately mixingtogether finely divided ore, fuel and water, blending with said mixturerecycle fines from a previous sintering operation and then subjectingthe `blended product to blast roasting at atemperature sucient to eiectagglomeration of said ore; said nes, said fuel and said waterrespectively constituting about to about 25%, about 2% to about 15%, andabout 5% to about 21%, by weight of said blended product, and saidblending step being carried out substantially at the end of said mixingoperation.

2. The method of sintering ores, which comprises intimately mixingtogether iin-ely divided ore,vfue1 and Water, blending with said mixturerecycle fines from a previous sintering operation and then subjectingthe blended product to blast roasting at a temperature sutlicient toeffect agglomeration of said ore; said lines, said fuel and said Waterrespectively constituting about to about 20%, about 7% to about 12%, andabout 16% to about 20%, by weight of said blended product, and saidblending step being carried out at the end of said mixing operation.

3. The method of sintering phosphate ores, which comprises intimatelymixing together nely divided phosphate ore, a carbonaceous fuel andwater, blending with said mixture recycle lines from a previousphosphate sintering operation and then subjecting the blended product toblast roasting at a temperature suicient to eiect agglomeration of saidore; said fines, said fuel and said water respectively constitutingabout 10% to about 20%, about 7% to about 12%, and about 16% to about20%, by Weight of said blended product, and said blending step beingcarried out substantially at the end of said mixing operation.

4. The method of sintering phosphate ores, which comprises intimatelymixing together in a pug mill finely divided phosphate ore, carbon andWater, blending with said mixture recycle nes from a previous phosphatesintering operation and then subjecting the blended product to blastroasting at a temperature sufficient to effect agglomeration of saidore; said tines, said fuel and said water respectively constitutingabout 10% to about 20%, about 7% to about 8%, and about 16% to about20%, by weight of said blended product, and said blending step beingcarried out at the end of said mixing operation.

5.-The method of sintering-phosphate ores, which comprises intimatelymixing together in a pug mill finely divided phosphate ore, coke andwater, blending with saidmixture recycle fines from a previous phosphatefsintering operation and then subjecting the blended product to blastroasting at a temperature sufficient toeect agglomeration of said ore;said tines, said coke and said water respectively constituting 15%,about 7% to about 8%, and about 18.5%, by weight of said blendedproduct, and said blending step being carried out at the end of saidmixing operation.

6. In the method of sintering phosphate ores, which comprises intimatelymixing together sinter feed components comprising finely dividedphosphate ore, carbonaceous fuel and Water, and then subjecting theresulting product to blast roasting at a temperature sutiicient to electagglomeration lof said ore, the improvement which comprises blendingrecycle lines from a previous phosphate sintering operation with saidmixture; said lines, said fuel and said water respectively constitutingabout 10% to about 20%, about 7% to about 12%, and about 16% to about20%, by weight of said blended product, and said blending step beingcarried out substantially at the end of said mixing operation.

References Cited in the le of this patent UNITED STATES PATENTS McAfeeJune 3, 1919 1,444,955 Davis Feb. 13, 1923 2,052,329 Wendeborn Aug. 25,1936 2,343,270 Agnew Mar. 7, 1944 2,412,104 Stewart Dec. 3, 19462,533,142 rRoyster Dec. 5, 1950 FOREIGN PATENTS Great Britain Feb. 26,1925 OTHER REFERENCES Min-

1. THE METTHOD OF SINTERING ORES, WHICH COMPRISES INTIMATELY MIXINGTOGETHER FINELY DIVIDED ORE, FUEL AND WATER, BLENDING WITH SAID MIXTURERECYCLE FINES FROM A PREVIOUS SINTERING OPERATION AND THEN SUBJECTINGTHE BLENDED PRODUCT TO BLAST ROASTING AT A TEMPERATURE SUFFICIENT TOEFFECT AGGLOMERATION OF SAID ORE; SAID FINES, SAID FUEL AND SAID WATERRESPECTIVELY CONSTITUTING ABOUT 5% TO ABOUT 25%, ABOUT 2% TO ABOUT 15%,AND ABOUT 5% TO ABOUT 21%, BY WEIGHT OF SAID BLENDED PRODUCT, AND